The shut-off valve located behind your washing machine allows you to turn the machine's water supply off and on. This is handy when you want to work on the washer or replace it without disrupting water usage in the whole house. Replacing a washing machine shut-off valve, however, will require you to turn off your home's water supply while working.
Turn off the water supply for your house. Locate the main water supply shut-off valve, which typically is installed next to the water meter. For a house, the valve will be installed in a concrete or plastic box somewhere in your yard. At an apartment or condo, the valve will be mounted in a box on the side of the building. Turn off the valve by turning it in the opposite direction from which it currently is set. Use a pair of pliers if necessary.
Unplug the washing machine from the electrical socket. Pull it away from the wall so you can manoeuvre behind it.
Hold a towel underneath the spot where the coupling from the washing machine hose meets the shut-off valve that you want to replace. Unscrew the coupling, using the pliers if necessary. Catch any water that spills out with a towel.
Fit an adjustable wrench around the hexagonal base of the shut-off valve. Turn the wrench counterclockwise. Do not use too much pressure, as you could damage the supply pipe. Spray liberally with penetrating lubricant, if needed, and allow it to soak in. Continue unscrewing until the shut-off valve comes off the pipe.
Clean the threads on the supply pipe with steel wool. Apply pipe-thread compound to the threads on the supply pipe.
Insert the new shut-off valve on the supply pipe. Thread the valve into position and tighten it by turning it clockwise with the wrench.
Wrap the outlet on the shut-off valve with plumber's tape. Reconnect the washing machine hose coupling and tighten it with the wrench.
Restore the water supply at the main by turning the valve in the opposite direction. Check the supply valve and coupling for leaks and tighten them as needed.
Return the washing machine to its original location. Plug in the washer's power cord.
You can purchase shut-off valves that will cut off the water automatically if they detect a leak. These are more expensive, but remove concerns about the washing machine leaking while you are away. These can be found at most plumbing supply and home improvement stores.
Use caution when working with water and electricity.